Significance of a Prolactin Level of 505 mU/L
A prolactin level of 505 mU/L is within the normal reference range for non-pregnant females (approximately 141-1410 mU/L when converted from ng/mL) and does not require further evaluation or treatment. 1
Understanding Prolactin Reference Ranges
According to the Endocrine Society and American College of Endocrinology, the reference ranges for serum prolactin are 1:
- Non-pregnant females: 3.0-30.0 ng/mL (approximately 141-1410 mU/L)
- Pregnant females: 10.0-209.0 ng/mL (approximately 470-9823 mU/L)
- Postmenopausal females: 2.0-20.0 ng/mL (approximately 94-940 mU/L)
When converting between units, the approximate conversion factor is 1 ng/mL ≈ 47 mU/L, though this can vary slightly between laboratories.
Clinical Interpretation
- A prolactin level of 505 mU/L corresponds to approximately 10.7 ng/mL, which falls well within the normal range for non-pregnant females.
- This level does not suggest hyperprolactinemia, which is typically defined as prolactin levels above the upper limit of the reference range.
- No clinical intervention is necessary for a prolactin level within the normal range.
When to Consider Hyperprolactinemia
Hyperprolactinemia would be considered if:
- Prolactin levels exceed 30 ng/mL (1410 mU/L) in non-pregnant females
- Prolactin levels exceed 20 ng/mL (940 mU/L) in postmenopausal females
- The patient presents with symptoms such as:
- Menstrual disturbances
- Galactorrhea
- Infertility
- Visual field defects (suggesting a pituitary mass)
Important Considerations in Prolactin Testing
- Laboratory variability: Different assays may have slightly different reference ranges 2
- Macroprolactinemia: A common cause of laboratory interference that can lead to falsely elevated prolactin readings 2
- Stress, sleep, exercise, and certain medications can transiently increase prolactin levels
- Time of day can affect prolactin levels, with higher values typically seen in the morning
Clinical Pitfalls to Avoid
- Don't assume that mildly elevated prolactin levels (up to 100 μg/L or 4700 mU/L) necessarily indicate a prolactinoma, as other sellar lesions can cause moderate elevations 3
- Avoid misdiagnosis by ensuring proper blood collection (ideally in the morning after fasting and avoiding breast stimulation)
- Remember that certain medications (especially antipsychotics, some antidepressants, and metoclopramide) can elevate prolactin levels
In summary, a prolactin level of 505 mU/L is normal and requires no further evaluation or intervention in the absence of clinical symptoms suggesting hyperprolactinemia.